Wajadu helps you note what you've been doing throughout the day. It tries to stay out of the way, popping up at set intervals to ask you what you've been working on since it last asked. For example, have it ask you every hour what you've been doing - it's easier than trying to remember everything you did for the entire day (or worse).
It's currently implemented as a windows .NET app, and requires the .NET 2.0 runtime.
The work that you log goes into the installation directory under a file called worklog.txt. It's a tab-delimited file that tracks the project, log start and end time, the amount worked, and the description of work.